1. Field of the Invention
The invention relates to an electric discharge lamp comprising:
a shell having an axis, which shell accommodates a starter and is provided, on an outside, with electric contacts which are to be connected to a power supply;
a hermetically sealed discharge vessel comprising electrodes in end portions, which electrodes are each connected to a pair of current conductors which issue from the relevant end portion to the exterior;
a cover which is fixed on the shell in a direction transverse to the axis, which cover is rigidly attached to the discharge vessel, the pairs of current conductors each being connected to the starter and to a respective electric contact.
2. Description of Related Art
Such a discharge lamp is disclosed in DE-A 33 33 294.
The known lamp comprises a shell which accommodates, apart from the starter for igniting the lamp, a ballast to limit the current flowing through the lamp during operation. The contacts of the shell are situated at an Edison-cap, i.e. a screw cap. The shell of the cap serves as a first contact, and a bottom of the screw cap which is isolated from the shell of the cap serves as a second contact. The ballast and the Edison-cap enable the lamp to be directly connected to the electric mains.
The discharge vessel and the cover of the known lamp are detachably secured to the shell. For this purpose, the discharge vessel is specially provided with axially directed, rigid pins, which come into contact with the ballast when the cover is placed on the shell.
A drawback of the known lamp resides in that the shell comprises a ballast, leading to much assembly work in the manufacture of the lamp and causing the lamp to be bulky. Another drawback of the lamp resides in that special, unusual, rigid pins must be provided at the discharge vessel. Yet another drawback resides in that the discharge vessel with the cover can be detached from the shell, so that arrangements must be made to ensure that all live parts in the shell are inaccessible to the user.
It is an object of the invention to provide an electric discharge lamp of the type described in the opening paragraph, the construction of which is simple, safe and readily reproducible.
In accordance with the invention, this object is achieved in that, for each pair of current conductors, a first and a second forked contact element facing the cover is attached in the shell, in which contact element a respective current conductor is tightly and inextricably fixed so as to extend transversely to the axis, and the contacts at the shell are pin-shaped and extend along the axis.
Owing to the pin-shaped contacts, the lamp cannot be directly connected, via a screw socket or bayonet socket, to the electric mains, but instead is applied using an external ballast which, for example, is accommodated in a luminaire. As a result, the construction of the lamp is comparatively simple, and the lamp is not very bulky.
In the assembly process of the lamp, the contact elements enable the shell and the cover with the discharge vessel to be united simply by pressing the shell and the cover against each other, and to simultaneously form electric connections, via the contact elements, between the current conductors on the one hand and the electric contacts on the other hand. This also enables the discharge vessel to be secured to the cover before the discharge vessel is electrically connected to the shell. Thermal processes, such as soldering electric connections and, for example, cementing for connecting the shell and the discharge vessel to each other, can thus be avoided in the final step in the manufacture of the lamp.
The forked contact elements are known per se as xe2x80x9cpiercing contactsxe2x80x9d. These forked contact elements comprise a metal plate, an edge of which is provided with a slit having a narrowing entry. A metal conductor, for example a wire, may be provided in the entry of the slit so as to extend transversely to the plate, whereafter said conductor is laterally pressed into the slit. The slit and the wire are dimensioned so that the contact element forms grooves in the conductor, resulting in a close and mechanically strong contact. If the connection is inaccessible to tools, the connection generally cannot be interrupted in a non-destructive manner and hence is inextricable.
In a favorable embodiment, the starter has current-supply wires, and the first contact elements comprise a forked portion, wherein the current-supply wires are tightly accommodated. This embodiment has the advantage that, for example, soldered joints between the starter and the contact elements are avoided.
It is possible that the contact elements were present when the shell was manufactured, as a result of which they are anchored in the shell. Advantageously, however, the shell has seatings and the contact elements are tightly accommodated in a respective seating. This has the advantage, inter alia, that the shell can be manufactured in a simpler mold.
Another advantage of said embodiment resides in that the forked portion accommodating the current-supply wires may be directed away from the cover. This has the advantage that if the starter is arranged in the shell prior to the contact elements, the electric connection between the contact elements and the starter is formed at the same time.
It is desirable for the lamp to comprise an anti-hum capacitor. In a modification, this capacitor having conducting wires is accommodated in the shell, and the first contact elements comprise a second forked portion facing away from the cover, in which forked portion the conducting wires are tightly accommodated. In the manufacture of this modification, the electric connections of the starter and the capacitor are simultaneously formed when the contact elements are provided.
In a favorable embodiment, the second contact elements are integral with the electric contacts. This embodiment has the advantage that making electric connections between the contacts and the second contact elements can be dispensed with.
The shell and the cover may be, for example, clamped together. It is attractive, however, if they are permanently interconnected. They may be attached to each other, for example, by local fusion or bonding using an adhesive. In an advantageous embodiment, however, the cover and the shell are secured to each other by means of a click-connection, in particular a concealed, i.e. invisible and inaccessible, click connection. In this case, the shell and the cover are interconnected in an assembly operation, i.e. without using thermal or other processes.
The discharge vessel may comprise, for example, a curved tube or various series-connected, curved or straight tubular portions. The discharge vessel may be connected to the cover by means of, for example, a cement or an adhesive, such as a UV-curing adhesive.
The contact elements may be made from, for example, phosphor bronze or stainless steel. The shell and the cover may be manufactured from a synthetic resin, for example a thermoplastic, such as polybutylene terephtalate.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.